As is known in the art, MMICs include a plurality of microwave transmission lines in close proximity one to another. A portion of one MMIC with a coplanar waveguides transmission line (CPW) and an adjacent microstrip transmission line is shown in FIGS. 1A and 1B; here shown with a scratch resistant dielectric layer over the transmission lines, as shown. More particularly, if the electrical isolation between two transmission lines is not greater than typically 20 dB more than the difference in the signal levels carried by the two transmission lines can result in unwanted feedback between the two transmission lines. One method used to solve this problem is to separate the center conductor of the microstrip transmission line from the outer edge of the proximate ground plane conductor of the CPW a distance D (FIG. 1B) sufficient to provide the requisite electrical isolation between the CPW and the microstrip transmission line. However such techniques use valuable surface area for the pair of transmission lines